This invention relates to the transmission over long distances of status information and more particularly relates to the transmission of critical equipment status information in a fast and yet reliable manner.
In the operation of electrical power distribution systems, it is often necessary to communicate information concerning the status of a portion of the transmission network from one substation to a second remote substation. Such a communication is particularly necessary when a malfunction occurs in a portion of the system and it is desired to provide that information to a remote substation so that some or all of the equipment in a remote portion of the system can be placed off-line to prevent the malfunction from damaging such equipment or spreading to other portions of the transmission network. In many cases, the sending and receiving substations are unmanned and therefore the detection of a fault condition and the transmission of the information concerning that fault condition must be accomplished automatically.
In order to prevent a malfunction in one portion of the transmission network from spreading to a second portion, it is necessary to transmit information relating to the occurrence of a fault condition rapidly. At the same time, however, the consequences of shutting down a high-voltage power transmission line unnecessarily make it necessary that the fault information be accurately and reliably transmitted so that false shutdown or "trip" signals do not occur. It is therefore an object of the present invention to provide a data transmission system that is capable of rapidly and reliably transmitting data indicative of the change of state of one of the monitored devices to a fault condition.
It is another object of this invention to provide such a transmission system that assesses the validity of received data and prevents the use of invalid data. The data output at the receiving end is only enabled upon reception of valid information for all of the monitored devices.
Certain transmission systems that now exist utilize a separate communications channel for each device that is being monitored resulting in a duplication of equipment. Therefore, it is also an object of this invention to provide a system that will transmit status data corresponding to all monitored devices over a single communication channel.